* Christoph Lameter <[email protected]> wrote:
> These location triggered during testing with KVM.
>
> These are fetches without preemption off where we judged that
> to be more performance efficient or where other means of
> providing synchronization (BH handling) are available.
>
> Signed-off-by: Christoph Lameter <[email protected]>
>
> Index: linux/include/linux/topology.h
> ===================================================================
> --- linux.orig/include/linux/topology.h 2013-09-12 13:26:29.216103951
> -0500
> +++ linux/include/linux/topology.h 2013-09-12 13:41:30.762358687 -0500
> @@ -182,7 +182,7 @@ DECLARE_PER_CPU(int, numa_node);
> /* Returns the number of the current Node. */
> static inline int numa_node_id(void)
> {
> - return __this_cpu_read(numa_node);
> + return raw_cpu_read(numa_node);
> }
> #endif
>
> @@ -239,7 +239,7 @@ static inline void set_numa_mem(int node
> /* Returns the number of the nearest Node with memory */
> static inline int numa_mem_id(void)
> {
> - return __this_cpu_read(_numa_mem_);
> + return raw_cpu_read(_numa_mem_);
> }
These are generic primitives used in quite a few places and it can easily
be a bug to use numa_node_id() in a preemptible section - and this patch
would hide that fact.
So the correct way to do it is to have checking in these and to introduce
raw_numa_node_id()/raw_numa_mem_id() and change eventual KVM (and any
other) preemptible-section use of numa_node_id() to raw_numa_node_id() and
explain why it's safe to do it.
Thanks,
Ingo
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